textproduct: Rapid City

KEY MESSAGES

- Cool with showers likely through Friday.

- Mild and seasonal Saturday.

- Warmer conditions begin Sunday and last through next week.

UPDATE

Issued at 933 PM MDT Wed May 20 2026

Showers will continue to dissipate this evening across western SD. Not much change to the previous forecast, just a few adjustments to pops, mainly to raise pops with tomorrow's upper low and cold front and add some timing. Decent setup for widespread rain across most of the FA Thur-Thur night. Showers and storms will develop across the northeast WY and western SD, INVOF the stalled frontal boundary. Showers and storms will shift east across western SD Thur afternoon. A few stronger cells capable of gusty winds and small hail will be possible. As the low shifts east, rain will develop across northeast WY and shift east through Friday. Rain may change to snow across southern Campbell County Friday night and the higher elevations of the BH with a dusting to an inch possible (not expected to stick to roadways). There is the potential for localized rainfall amounts approaching an inch at areas that see storms tomorrow then rains overnight. System will move out Friday breezy with NW winds expected. Warming up and drying out after, although lingering cold pool aloft and LL moisture could support isolated showers over the Black Hills Sat afternoon.

DISCUSSION

(This Evening Through Wednesday) Issued at 1238 PM MDT Wed May 20 2026

Upper level analysis has a long wave trough extending through the Rockies into the Desert Southwest. At the surface, a lee trough extends through central Wyoming and a cold front extends from a surface low in southern Saskatchewan into the Pacific Northwest. Radar has a few showers across southwestern and south-central South Dakota.

For this afternoon and tonight, the lee trough will move into the forecast area and energy from the approaching trough will combine with increasing low-level moisture to support a few isolated showers and thunderstorms. NBM washed out these features, so decided to broad-brush 20 pops over the northern/central Black Hills. Showers will quickly dissipate after sunset with the loss of diurnal heating.

There will be a break in the precipitation overnight and into Thursday morning. Chances for showers will return by midday Thursday as the upper trough approaches the area. Diurnal heating combined with sufficient moisture will support convection initiating along the trough and the Black Hills. Showers and isolated thunderstorms will continue into Friday as the main trof axis moves through. NBM probabilities for precip >= 0.25" has a wide swath of 60 to 80 percent over most of western SD, excluding far northwestern SD and the plains of northeastern Wyoming. Based off the current track of this system, highest QPF amounts are expected in the Black Hills, southwestern, and south-central South Dakota.

The upper ridge slowly rebuilds over the weekend, allowing for a return of warm temperatures. Additionally, strong thunderstorms may be possible Tuesday and Wednesday next week.

AVIATION

(For the 12Z TAFS Through 12Z Friday Morning) Issued At 504 AM MDT Thu May 21 2026

A cold front will move through the region today with gusty northerly winds behind it. A disturbance moving over the area will combine with the cold front to produce shra over northeastern WY this morning, shra/TS this afternoon/early evening, and then rain for the rest of the forecast period. Some snow will occur over the higher elevations of the Black Hills. The result will be MVFR/IFR conditions slowly moving from northeastern WY into the Black Hills today. Then tonight, widespread MVFR/IFR conditions will develop over western SD with local LIFR conditions over the Black Hills.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.